R.A. Yingst, F.C. Chuang, D.C. Berman, S.C. Mest A reassessment of the volcanic history of western South Pole-Aitken Basin based on geologic mapping R.A. Yingst, F.C. Chuang, D.C. Berman, S.C. Mest Geologic map at 1:250,000 of Lunar Quadrangle 29-Planck Geological Society of America – Denver, CO, October 2013

Overview Geologic setting of the mapping site. Methodology; criteria for identifying volcanics. Implications More diverse modes of emplacement Greater area covered by volcanics Geological Society of America – Denver, CO, October 2013

LROC WAC mosaic of Planck Quadrangle Planck Quadrangle (outlined in black), with large impact structures noted. Map was created at 1:2,500,000-scale. Geological Society of America – Denver, CO, October 2013

Datasets LROC WAC mosaic of Jules Verne, Planck Quadrangle (~100 m/pxl) Clementine multispectral mosaic of Jules Verne (~100-300 m/pxl) LOLA topographic of Jules Verne (~1 m/pxl vertical) Clementine multispectral ratio: 750/415 and 415/750 are shown in red and blue respectively – these tones indicate the continuum slope, that we interpret to suggest freshness (blue) or maturity (red) to the soil. 750/950 is shown in green; since 950 is around the 1 micron band for Fe absorption, the stronger this ratio is, the greener the signal is. N 15 km Geological Society of America – Denver, CO, October 2013

Volcanic deposits Volcanic deposits identified by albedo, texture, morphology and spectral signature. - Mare deposits - Pyroclastics • Other volcanically derived deposits - Cryptomare candidates Geological Society of America – Denver, CO, October 2013

Geological Society of America – Denver, CO, October 2013

Mare deposits Pauli N 12 km Smooth, low-albedo surface materials with relatively sharp boundaries and elevated mafic content. Here, LRO WAC image (a) and Clementine color ratio image (b) of Pauli crater, with an example of a mare deposit in the floor. The mare material embays an older impact structure along Pauli’s south rim. Smaller craters that post-date mare emplacement have excavated Fe-rich material, which can be seen as green-toned ejecta in (b). N 12 km Geological Society of America – Denver, CO, October 2013

Pyroclastic deposits N Jules Verne N 20 km Rougher surface deposits, very low albedo, diffuse or irregular boundaries, elevated mafic content (Figure 3). Here, LRO WAC image (a) and Clementine color ratio image (b) of northwest Jules Verne crater floor, with an example of a pyroclastic deposit associated with a fracture or graben. The deposit is lower albedo than the surrounding material. Note the color difference between the mare material covering the basin floor (younger craters have excavated Fe-rich material) and the darker, redder pyroclastics that appear similar to the Group 2 deposits of [5]. N 20 km Geological Society of America – Denver, CO, October 2013

Other volcanically-derived deposits Jules Verne P N N 7 km Floor-fractured craters (right crater is Jules Verne P), as imaged by the LRO WAC (a) and Clementine (b). Floors are disrupted by a series of sub-concentric fractures. Fractures have a strong signature in the 750/950 nm ratio, indicating Fe-rich material. Other volcanically-derived deposits 7 km Geological Society of America – Denver, CO, October 2013

Other volcanically derived deposits Jules Verne N 5 km Rille (yellow arrow) and flow (red arrow) in Jules Verne crater, imaged by the LRO WAC (a) and Clementine (b). Note that the boundary between dark, smooth mare material and rougher highland (blue arrows) can also be seen as differences in yellow-green tones in (b). Other volcanically derived deposits 5 km Geological Society of America – Denver, CO, October 2013

Cryptomare material N of Planck N 15 km Heightened mafic content that otherwise showed little or no morphologic indication of volcanic origin (Figure 4). Here, LRO WAC image (a) and Clementine color ratio image (b) of a candidate cryptomare deposit, a crater northwest of Planck. Morphology in (a) is smooth, but albedo is higher than mare material. Fresh craters smaller than ~ 1 km do not excavate Fe-rich (green-toned) material, while northern craters larger than this diameter do. The implication is that older, obscured mare material may lie underneath a younger layer, at least in the north of the crater. N 15 km Geological Society of America – Denver, CO, October 2013

Geological Society of America – Denver, CO, October 2013

Results 22 mare deposits, 18 other volcanic deposits (7 are newly mapped). An additional 3,000-5,000 km2 covered by other volcanics (5% more). Broader range of volcanic expressions than previously mapped. Geological Society of America – Denver, CO, October 2013

Conclusions Greater surface area covered by volcanics implies a greater volcanic flux. More variations in eruptive style than previously suspected — We infer mode of emplacement of volcanic deposits (an indication of conditions at depth) was more diverse than previously thought. Other volcanics associated with fractures — tectonic trigger? No estimate yet on the stratigraphy of these deposits and how morphology varies as a function of time. Geological Society of America – Denver, CO, October 2013